On top of this, some of the PageSpeed tips might be a good idea.
It's weird other people's browsers aren't loading this from cache. My Chrome browser is loading from cache just fine:
(get request)
GET /uploads/showdown/2013_08/thumb-sss_96849afd5ab376ff7e5d536eeb844fbf.gif HTTP/1.1
Host: www.gamedev.net
Connection: keep-alive
Cache-Control: max-age=0
Accept: image/webp,*/*;q=0.8
Pragma: no-cache
If-None-Match: "2b8bc3-3067776-4e308fd043ec0"
If-Modified-Since: Sat, 03 Aug 2013 11:00:51 GMT
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_8_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/28.0.1500.95 Safari/537.36
Accept-Encoding: gzip,deflate,sdch
Accept-Language: en-US,en;q=0.8
Cookie: [...]
(response)
HTTP/1.1 304 Not Modified
Last-Modified: Sat, 03 Aug 2013 11:00:51 GMT
ETag: "2b8bc3-3067776-4e308fd043ec0"
Cache-Control: max-age=604800
Expires: Fri, 16 Aug 2013 12:59:42 GMT
Content-Type: image/gif
Server: GDNET
Accept-Ranges: bytes
Date: Fri, 09 Aug 2013 22:27:53 GMT
Connection: keep-alive
X-Cache: HIT
X-Cache-Hits: 7894
X-Success-Kid: Linked from Reddit.. Didnt Crash